A server device which holds a plurality of server modules in a chassis and controls the temperature of the inside of the chassis with a built-in fan is known.
For example, Patent Document 1 discloses a computer system which has a plurality of fans and two fan controllers. According to Patent Document 1, the two fan controllers monitor all the fans, and each of the fan controllers is configured to increase the speed of rotation of a fan controlled thereby when detecting a failure of a fan controlled by the other fan controller. Such a configuration can secure high reliability.    Patent Document 1: United States Patent Application Publication No. US 2004/0130868
As disclosed by Patent Document 1, it is general to equip a server device with two fan controllers (chassis management modules which control fans) for securing reliability and thereby make fan control redundant.
However, redundant chassis management modules such as fan controllers need extra costs. Therefore, in terms of costs, it is desirable to reduce the number of chassis management modules. On the other hand, if a server device has only one chassis management module, a failure of the chassis management module brings the device to an uncontrollable state. Therefore, in terms of reliability, it is not desirable to reduce the number of chassis management modules.
Thus, for a server device, reduction of the number of chassis management modules is desirable in terms of costs, but reduction of the number of chassis management modules is difficult in terms of reliability. In other words, a server device has a problem that it is difficult to reduce costs while securing reliability.